Retinal ischemia occurs when the oxygen and glucose supply to the retina is interrupted, as in retinal vascular diseases, such as retinal artery occlusion, or as a result of systemic diseases such as diabetes mellitus. The pathophysiology involves changes in cellular biochemistry or energy level, blood flow, and gene expression. During the first eight years of this project, extensive biochemical, functional, structural and retinal hemodynamic evidence has been obtained to support the major, but complex involvement of the purine nucleoside adenosine in retinal ischemia-reperfusion injury. In addition, the phenomenon of retinal ischemic preconditioning was demonstrated, whereby a brief period of non-damaging ischemia 24 or 72 h before more prolonged ischemia completely preserved retinal function and morphology, and prevented post-ischemic decreases in retinal blood flow. Adenosine, protein kinase C (PKC), potassium ATP channels, and de novo protein synthesis are involved in this endogenous protective phenomenon. Proposed experiments will use biochemical, functional and morphological measurements to examine the mechanisms whereby adenosine initiates ischemic preconditioning, the role of protein kinase C, and the signal mediators linking adenosine, the cell nucleus, and preconditioning. The long-term goal of the project is to further characterize the endogenous protective mechanisms against ischemic injury in the retina, and ultimately use this knowledge to develop clinically relevant treatment strategies of retinal ischemic diseases. The first aim will characterize early triggering events, signal transduction factors, and the role of adenosine in initiating preconditioning. The second characterizes the involvement of PKC, and its interaction with adenosine in this neuroprotection. The third will examine the effect of ischemic preconditioning on protein phosphorylation, characterize some of the major molecular intermediaries in preconditioning, and the relationship between these factors and adenosine. The powerful effects of endogenous neuroprotection suggest that these experiments could lead directly to clinically useful treatments for retinal ischemic diseases.